It is proposed to use Brugia malayi (subperiodic strain) infection in the ferret, Mustela putorius furo as an experimental model for the study of immunobiology and pathology of lymphatic dwelling filariae. The study will elucidate the immunologic mechanisms responsible for occult infection by determining the antibody response promoting clearance of microfilariae, for inducing the characteristic inflammatory responses to microfilariae and the immunoregulating factors which may modulate the cellular responses to microfilariae typical of occult infections. A histologic and ultrastructural study will be done to determine the development and composition of the characteristic lesions of occult filariasis, the Meyers-Kouwenaar body. The ferret will be evaluated as an experimental host for the study of transient lymphatic disease and chronic obstructive disease following small repeated inoculations of infective larvae. The development and duration of lymphatic disease will be correlated with immunologic responses including changes in immediate and delayed hypersensitivity to parasite antigens. The proposed study is designed to identify mechanisms in immunopathogenesis in occult infections and lymphatic disease in filarial infection and should contribute to understanding the disease in man and have eventual application to treatment and prevention of human disease.